Abstract: The automatic injection device of the invention comprises an injection syringe having a syringe body provided with a lateral injection-liquid supply tubulure, retention means for retaining the animal to be treated, enabling the latter to be placed in a given transverse position and at a given angle with respect to the syringe, syringe displacement means for advancing and withdrawing the syringe at each injection, and piston displacement means for displacing the piston with respect to the syringe body. Such a device enables for example about at least 2000 chicks to be vaccinated per hour, while at the same time ensuring a dosing accuracy on the order of 1/100 and an exact location of the point of injection.